Which of the following types of cryptography should be used when minimal overhead is necessary for a mobile device?

Block ciphers are symmetric encryption algorithms that process data in fixed-size chunks and do not address asymmetric key exchange or digital signature overhead on constrained devices.

ECC achieves security comparable to RSA using significantly smaller keys - a 256-bit ECC key offers roughly equivalent strength to a 3072-bit RSA key. This dramatically reduces CPU cycles, memory consumption, and power usage, which are critical constraints on mobile hardware. For this reason, ECC is the preferred asymmetric cryptographic algorithm for mobile and embedded environments where overhead must be minimized.

The Diffie-Hellman algorithm depends on large prime number arithmetic, making it computationally expensive relative to ECC for equivalent security levels.

Stream ciphers encrypt data one bit or byte at a time and are efficient for symmetric bulk data encryption, but they do not replace asymmetric operations like key exchange or authentication.